1. Field of the Invention
This invention relates to a method of producing caking coal from non-caking or weakly caking coal. As is well known, caking coal or strongly caking coal is essential to production of coke used for iron manufacture. The price of caking coal has risen annually and presents the iron manufacturing industry with a serious problem. The worldwide caking coal or strongly caking coal reserves are very limited as compared with non-caking or weakly caking coal reserves and total depletion of such caking coal reserves is even considered likely in the near future. By the present invention the inventors intend to provide a means for coping with this situation by a method for obtaining (from non-caking or weakly synthetic caking coal) caking coal which compares well in quality with natural caking coal.
Caking coal and non-caking coal differ widely from each other in both physical and chemical properties. As regards the chemical composition, a striking difference is seen in oxygen content. For example, the oxygen content of Yallourn coal, which is a non-caking coal produced in Australia, is as high as 28% whereas that of strongly caking coals produced in the U.S. is as low as 2 to 3%. Oxygen content of weakly caking coals produced in Japan is within the range of 6 to 8%. Various attempts have been made to obtain caking coal by removing or reducing oxygen in non-caking coal down to the level of caking coal, but no successful result has been reported.
This invention has been accomplished on the basis of the discovery that caking coal can be produced from non-caking or weakly caking coal by first liquefying raw coal by hydrogenation and then subjecting the thus treated coal to heat polymerization.
2. Description of the Prior Arts
Liquefaction of coal has been known and practised since before the 2nd World War, and more recently deeper studies on this subject have been carried out, in the United States and Germany and some significant results have been made public. The basic techniques for liquefaction of coal were already completely worked out before the 2nd World War, and at present, studies are being made for improvement in the minute details. No specific techniques are required for liquefaction of coal used in the present invention, but any known coal liquefaction technique can be employed.
As Japan depends almost entirely on imports from foreign countries for its supply of caking coal, efforts have been concentrated on methods for obtaining equivalents of caking coal by polymerizing or pyrolizing heavy oil residue which are abundantly available in Japan, and some successful results have been made public. However, there is not yet known any method for obtaining caking coal by liquefying raw coal and then polymerizing the liquefied product.
Regarding to polymerization of heavy oil residuum, the following literature is available:
1. Cokes Circulars 23, No. 2, pp 77- 81 (1974) by K. Kiritani et al.: "A Study on Application of Petroleum Heavy Oil to Metallurgical Coke".
2. Journal of the Fuel Society of Japan, 51, No. 544 (Aug. 1972) by Y. Kiritani et al.: "Production of Improved Strongly Caking Coal from Specific Petroleum Pitch".
The above-mentioned reference No. 1 discloses the fact that petroleum heavy oil can be used as raw material for metallurgical coke, by examining heavy oil heat treatment conditions and fluidity of specimens using a plastometer. Reference 2 shows the fact that an improvement of quality of coke can be attained by first subjecting raw oil to a short-time decomposition treatment at a temperature of about 2,000.degree. C., then blending the obtained specific pitch as caking agent in an amount of 20 to 40% in non-caking coal, and then subjecting the mixture to hot briquetting.
There has however not been known a method for obtaining synthetic caking coal by liquefying raw coal and then heat-polymerizing the liquefied coal.